Various types of inhalers for delivering a medicament are known. For example, U.S. Pat. No. 3,938,516 (Mathes No. 1) discloses an inhaler for delivering a powdered medicament. The device includes a mouth piece 14 which has provided therein an emptying chamber. A longitudinally extending passageway for introducing air into the inhaler is connected to the passageway. The inhaler also includes a hollow air stream tube which extends preferably into an opened capsule containing a medicament. Upon inhalation, air drawn through the air stream tube into the capsule assists in causing the medicament to be expelled therefrom.
Mathes No. 1 states at column 4, lines 32-45, that "Quite obviously, no single device will be suitable for all persons requiring administration of powdered medicaments since, for example, people with differing lung capacities are known to generate flow rates from about 30 liters/minute or so to about 120 liters/minute or so through inhalation devices of this and known types. Nonetheless, the device of [Mathes No. 1] affords such variability, through proper selection of the various design parameters, that a device, embraced with the scope of [Mathes No. 1], can be designed for a particular patient-generated flow rate to deliver the medicament according to a certain set of pre-determined objectives (e.g., slow or fast administration, one or more inhalations etc.)."
Accordingly, one of the disadvantages of Mathes No. 1 is that a single device is not capable of being used with a variety of patients. In some cases, the inhaler may be required for treating an individual who has a diminished lung capacity. For example, an individual who may need to use the device may suffer from, for example, emphysema or asthma, and may not be able to generate a high flow rate of air. Therefore, the device of Mathes No. 1 would have to be designed for someone who could only administer a dose slowly due to their diminished lung capacity. Alternately, the device may be used by someone who does not have a diminished lung capacity. Unless the device is properly designed, the medicament will exit the inhaler at a rate such that a portion, if not substantially all of the medicament, will impact upon the throat and airways of the user and therefore not be drawn into the lungs for absorption.
A further disadvantage of Mathes No. 1 is that, over the course of a single inhalation, the concentration of the medicament in the air inhaled by a user is uneven. This arises for two reasons. First, once the medicament is withdrawn from the container, it is immediately transported through the inhaler into the mouth or nose of the user. Therefore, little mixing of the medicament in the air inhaled by the user occurs. This results in uneven distribution of the powder in the air inhaled by the user and, to the extent that the medicament is drawn into the lungs of the user, the medicament will not be distributed evenly throughout the lungs. Secondly, a substantial portion of the medicament may be withdrawn from the medicament container and entrained in the air upon initial inhalation. Accordingly, the medicament will not be distributed throughout the entire lung of the user but will be concentrated in that portion of the lungs of the user to which the first portion of the air inhaled on inhalation travels. (See also U.S. Pat. No. 4,014,336 (Mathes No. 2); U.S. Pat. No. 4,005,711 (Glen No. 1); and U.S. Pat. No. 4,098,273 (Glen No. 2).) In Glen Nos. 1 and 2, a deflector surface is used to direct a portion of the incoming air into the medicament container so as to entrain the medicament in the air which is inhaled by a user.
U.S. Pat. No. 3,964,483 (Mathes No. 3) and U.S. Pat. No. 3,973,566 (Mathes No. 4) each disclose a device wherein the air entering the inhaler is not aimed directly at the medicament in a medicament container. Instead, turbulent air flow is created so as to draw the medicament out from the container. These devices have the same disadvantages as Mathes No. 1.